1. Field of the Invention
The present invention relates to a vehicle-mounted alarm generating apparatus for alarming a driver of a vehicle when there is a possibility that the vehicle is deviating from the lane in which the vehicle is running.
2. Description of Related Art
There is known a vehicle-mounted apparatus configured to extract a boundary line (a road center line, a road side line, a lane line, for example) on the road on which the vehicle is running from an image of the scene ahead of the vehicle, calculate a time needed for the vehicle crosses the boundary line on the basis of the distance (lateral distance) between the vehicle and the boundary line and the lateral speed of the vehicle, and issue an alarm depending on the calculated time. For example, refer to Japanese Patent No. 3486924.
Incidentally, road markings to show lane boundaries (referred to as “road boundary marking” hereinafter) include not only a boundary line but also a safety zone (zebra zone) as shown in FIG. 6. Furthermore, a boundary line is not limited to a single-line marking. As shown in FIGS. 5A to 5D, a double-line marking or a triple-line marking having a relatively large width may be used as a boundary line. In the following, a road marking having a relatively large width such as a zebra zone, double-line marking or a triple-line marking is referred to as a “wide boundary marking”.
The conventional apparatus as disclosed in the above-mentioned patent has problems in that the generation timing of an alarm varies depending on which position of such a wide boundary marking is used as a reference position, and that it is not possible to generate an alarm at an appropriate timing whichever position of the wide boundary marking is used as the reference position, as explained below.
In a case shown in FIG. 6, when a time at which a vehicle reaches a wide boundary marking (see M1 in FIG. 6) is set as an alarm generation timing, no alarm is generated at a time when the vehicle has crossed the wide boundary marking (see M2 in FIG. 6) although the vehicle is about to enter another lane at this time. On the other hand, when a time at which the vehicle runs through the wide boundary marking is set as an alarm generation timing, no alarm is generated at a time when the vehicle reaches the wide boundary marking although the vehicle is about to run off the lane at this time.
It may occur that both of the above times are used as an alarm generation timing. However, in this case, since a similar alarm occurs twice although the degrees of danger are different between these timings, there is a possibility that the driver's attention to the alarm is lowered.